Structure and morphology of magnetron sputtered W films studied by x-ray methods

The structural and morphological studies of a number of tungsten (W) thin films were carried out using grazing incidence x-ray diffraction, x-ray reflectivity and grazing incidence small-angle x-ray scattering. The W films were prepared by magnetron sputtering in an Ar atmosphere at various pressures and with different powers applied to the W target. We find films with metastable β-W or amorphous phase in the form of nano-columns when deposited at high Ar pressure (>5 mTorr) or with low sputtering power (<20 W), respectively. The appearance of the metastable β-W phase is related to the lowered deposition flux of W atoms, increased film porosity and correspondingly to the higher probability of oxygen incorporation. In films with only the β-W phase we find up to 50% reduction in mass density compared with the density of bulk tungsten. The nanoporosity of the W films is discussed in terms of self-shadowing effects. (paper)